Sheath for explosives



March 7, 1950 l. c. WOOD 4 9,4 0

SHEATH FOR EXPLOSIVES Filed Jan. 27, 1945 Iver C. Wood INVENTOR.

ATTORNEY Patented Mar. 7, 1950 UNITED ST FFICE SHEATH F013 EXPLOSIVESIver C. Wood, Denver, olo., assignor to The Denver Fire Glay Company,Denver, 0010., a

corporation of Delaware 3 Claims.

This invention relates to sheaths for stick explosives and moreparticularly relates to sheath assemblies applied to dynamite cartridgesfor flame quenching, cushioning, and/or similar purposes.

In using explosives in underground mining operations, it frequently isdesirable to enclose the explosive charge and particularly dynamitesticks in a composition of the type having flamequenching properties, inorder to minimize the danger of igniting gas pockets in the deposit.Also, to increase the production of lump coal by reducing the amount ofshattering, it is sometimes desirable to cushion the effect of the blastand the covering compositions may be utilized to perform this functionas well.

Regulations in some states require the use of encased dynamite inunderground operations and the explosive manufacturers have developed anumber of different types of casings for the stick explosives. Variouscombinations of ingredients have been developed which are satisfactoryfor the intended purpose, but the development of a satisfactory methodfor forming such compositions into a satisfactory casing presents manydifliculties.

One method which has been used involves the steps of forming theingredients into a wet mass and then subjecting this mass to anextruding operation to produce the casings of required contour andthickness. However, any considerable amount of moisture in the casingwill have deleterious effects on the explosive, causing it to set, anddecreasing its strength and sensitiveness. As the aforesaid extrudedmaterial has too high a moisture content to be placed immediately incontact with the explosive composition, a drying operation is required,

If rapid drying is employed, the temperatures attained have adestructive effect on the flamequenching ingredient, such as sodiumbicarbonate, which render the composition unsuited for its intendedpurpose. If natural drying or slow, artificial drying is resorted to,the storage, equipment and handling costs of such an operation place anexcessive cost on the finished article.

Binders of bituminous material capable of being softened by heat havebeen used to render the sheath plastic and moldable. This type of binderhowever has the disadvantage of being combustible and productive ofpoisonous gases upon detonation.

Another expedient that has been attempted is to provide a paper cylinderin which an explosive stick of lesser diameter is inserted and then thespace between the stick and the cylinder is filled with theflame-quenching composition. This operation involves maintaining thecomposition in loose condition while filling and even when Well packedin this operation, the composition does not have sufficient rigidity tosatisfy the requirements for transportation and installation.

Paper sheaths impregnated with Water-soluble cooling salts and designedto be wrapped around the dynamite cartridge are also known to the priorart. These likewise have the disadvantage of being largel combustibleand adding to the toxicity of the fumes.

It is an object of the present invention to provide a simple, durableand efficient sheath for stick explosives which possesses sufficientstability to satisfy all the usual requirements for transportation andinstallation and which has a very low mo sture content.

Another object is to provide a moldable sheath of such form andcomposition that it may be molded in a substantially dry state requiringno subsequent drying.

Still another object of the invention is to pro- Vide a novel type ofsheath for stick explosives which facilitates the sheath encasingoperation, whether performed manually or by machine.

A further object of the invention is to provide a. sheath of reasonablylow density for stick explosives which provides a substantially rigidcasing therefor of substantially uniform thickness and compositionthroughout its length.

Still another object of the invention is to provide a novel design ofsheath for stick explosives which may be transported to a place of usein a substantially fiat position to conserve shipping space and whichassumes a tubular shape in use.

Other objects reside in novel details of construction and novelcombinations and arrangements of parts, all of which will be fullydescribed in the course of the following description.

A variety of compositions may be selected as suitable for the practiceof the present invention. Funct onally, the ingredients comprise aflamequenching ingredient, a filler material and a binder. Sodiumbicarbonate is Well suited for the flame-quenching effect and many ofthe regulat ons require that it be present in the composition in aquantity not less than 50% of the total content. Other flame-quenchingsalts which may be used for this purpose include sodium chloride. borax,sodium thiosulfate, and ammonium sulfate,

In order to minimize the amount of noxious 3 fumes, i. e. carbonmonoxide, produced upon detonation, the ingredients of the sheath shouldbe essentially non-combustible. Not more than about to carbonaceousmaterial may be used, as amounts appreciably greater than this wouldprobably cause the blasting assembly to produce more noxious gases upondetonation than are allowed by the U. S. Bureau of Mines for apermissible explosive. From about 5% to about 10% of bulky, fibrouscarbonaceous material such as sugar cane bagasse, wood pulp, straw,cotton fibres, etc., are desirable as ingredients of my sheath as theyadd bulk and achieve the result of binding the powdery ingredientstogether.

The filler should be essentially inert and noncombustible and maycomprise clays such as bentonite or gaolin, minerals such as vermiculiteor expanded mica, expanded perlite or pearlstone, fullers earth ordiatomaceous earth, asbestos, pumice, or manufactured bulky fillers suchas expanded sodium silicate or silica bubbles, rock wool, mineral wool,glass wool, or specially prepared smelter slag.

The binder which cements the dry pulverulent materials together may bedextrine, sodium silicate, glue, cement, plaster of Paris, or claymoistened with a little water. I have found that the mixturecomprisingsodium bicarbonate, expanded vermiculite, bentonite, bagasse,and dextrine, moistened with a little water has excellent bindingproperties when essentially dry, probably because of the flexible natureof the flakes of ver- Iniculite which appear to interlock and hold theentire mass together.

A suitable-combination. of such ingredients is selected for forming thesheath. This is presented forillustrative purposes only and it is notintended that I be limited'thereby. For example, a com ositioncomprising 52% sodium b carbonate, 2l expanded vermiculite, Mi /2%bentonite and 10% bagasse may be thoroughly intermixed, and then 95parts of this mixture may be mixed with 5 parts of water to form apliable mass.

This mass is placed in suitable molds and compressed into the shapesconstituting the sheaths of the present invention. Hence, the termsmolde and molding as used herein are intended to cover compressingmaterial in a mold as well as molding or shaping plastic material. Thefeatures of the mold assembly and operation comprise a separateinvention, for which reason they have not been shown and described heren. This working of the mass as aforesaid, results in some natural dryingand by the time the sheath members are completely formed, their moisturecontent is within the limits prescribed for such articles and nosubsequent drying is necessary or advisable.

The accompanying drawings illustrate typical embodiments of the presentinvention and the practice of the invention will be best understood byreference thereto. In the drawings, in the several views of which likeparts have been designated similarly,

Fig. i is a broken side elevation of a stick explosive encased in asheath embodying features of the present invention;

Fig. 2 is a section taken along the line 2-2, Fig. 1;

Fig. 3 is an end elevation of a sheath embodying features of the presentinvention with a stick explosive supported thereby and illustratingstages of the encasing operation;

Fig. 4 is a perspective view of a sheath con- 4 structed in accordancewith the practice of the present invention; and

Fig. 5 is a perspective view of another form of sheath constructed inaccordance with the practice of the present invention.

As shown in Figs. 1 and 2, the article sold in commerce and used inblasting operations comprises a stick explosive E encased within atubular sheath S and held by a wrapping W of paper or similar materialfastened as by folding its ends, by gluing, or in any other suitablemanner.

The sheath S comprises three segmental sections 6, 1 and 8, each ofsubstantially equivalent dimension, and held together along adjoiningedges by acommon portion 9. In assembling the unit shown in Fig. 1, thesheath S is placed on the wrapping member W as shown in Fig. 3, and theexplosive cartridge E is placed on the intermediate section 1, afterwhich the sections 6 and 8 are folded upwardly to form the tubularenclosure indicated by the dotted line positions, sections it, 7 and 8thereby being detaohed from each other by rupture of their commonportions 9, and the wrapping member is next wrapped around the sheathand its ends folded or is otherwise sealed to complete the enclosure.Alternatively, the segmental sections may be folded around the dynamitecartridge and the whole encased in a preformed paper tube.

Under some circumstances, it will be preferable to employ a four-sectionsheath and such a sheath S is shown in Fig. 5. The end sections 5' and 8enclose two intermediate sections la and ib, and the'adjoining sectionshave common portions 9 maintaining the' integral character of the unit.

In all the forms, the tubular sheath provides an adequate degree: ofrigidity to satisfy the requirements, and-bymaintaining the low moisturecontent during the forming operation, the sheath is ready for use assoon as it leaves the mold. When it is necessary to ship the sheaths toa distant point of assembly they can be nested to gether and packaged inan essentially flat condition to conserve shipping space.

In the moisture content control, it has been found that if the moisturetransfer to a stick explosive is'not appreciably over 1% by weight ofits content, the aforementioned deleterious effects do not result.Consequently, if the moisture content of the sheath at the time offormation does not exceed 10% and preferably is held to about 5%, theamount of moisture transfer resulting from its subsequently beingmaintained in contact with the stick explosive will not exceed thepermissible 1% limit.

While the drawings illustrate 3 and 4 section arrangements, it will beapparent that a lesser or a greater number may be used. However, whenatwo-section arrangement is used, it is diflicult to maintain theuniformity of th ckness or density that is attainedwith a flattersection. I have found that when only two semi-circular segmentalsections are used the sheathing mixture is not distributed uniformly inthe pressing operation and defective fragile sheaths result which varyin thickness and density. In all the preferred forms, the interiorsurface of the sheath is so shaped that when the sections are foldedinto a tubular enclosure, the inner wall thereof is substantially a truecircular contour and can be drawn into close fitting or snugrelationship to the cartridge.

In all these forms, the various enumerated ingredients may be selectedto vary the compositions within prescribed limits to produce sheathshaving the aforesaid properties, and so long as the moisture content isheld within the prescribed limits the sheaths are adapted to be used assoon as formed.

When an explosive of the type shown in Fig. 1 is used in undergroundblasting operations, as in coal mining, a hole is drilled or otherwiseformed in the structure, into which the explosive is to be inserted. Thepowder man prepares the explosive for firing by punching a small hole inthe end of the cartridge, into which an electric blasting cap isinserted. Sand, clay, or other inert material is tamped in front of theexplosive through the outer end of the hole. The charge is then fired byelectricity, and in the resulting blast, the sheath, and particularlyits sodium bicarbonate content, smothers or dampens the flame withoutundue diminution of the force of the blast. The hot gases resulting fromthe explosion of the dynamite are thus cooled, not only by reason of theheat taken from them and utilized in the decomposition of the sodiumbicarbonate to sodium carbonate, water, and carbon dioxide, but also byabsorption of heat by the inert ingredients of the sheath.

The aforesaid sheath designs provide an integral mass of material ofsubstantially uniform composition and thickness encasing the explosive.Consequently, when only a cushioning effect on the blast is desired, thecomposition may be changed by substituting more filler for theflamequenching ingredient and forming the sheath with thinner walls orsegments. When dynamite is enclosed in a sheath of the nature describedand fired in a borehole, or simply surrounded by a cushion of air aswhen it is loaded in an oversize borehole, the disruptive effects of theexplosive in the immediate vicinity are much lessened. This has thepractical effect of reducing the shattering of the coal and increasingthe percentage of large sizes of lump coal blasted down. Sometimes it isdesirable to cushion the shot in this manner to take advantage of thehigher selling price of prepared sizes of coal.

It will be understood that the ingerdients selected for formation of anyof the above-described sheaths must be substantially inert, at least tothe extent that they will not react with each other, even whenmaintained in intimate contact over protracted periods. At the same timethe sheath ingredients must have no deleterious effect on the explosiveitself which is in close juxtaposition, separated from the sheath onlyby the original explosive cartridge wrapper. The preferred compositionpreviously described satisfies these requirements as it is substantiallyinert at normal atmospheric temperatures.

The preceding description and the accompany- 6 ing drawings are intendedto disclose typical ex- 0 amples of the practice of the invention, thescope of which is set forth in the hereunto appended claims.

What I claim and desire to secure by Letters Patent is:

l. A molded sheathing for an explosive cartridge comprising a flamequenching composition formed into a plurality of cylindrical segmentswith their outer convex surfaces tangent to a common plane, saidsegments being of substantially uniform thickness and integrally joinedalong their contiguous outer edge portions, the inner concave surfacesof said segments being separated by a V-shaped groove, each of saidinner surfaces comprising a like fractional portion of a circularcylinder, said sheath being adapted to be broken along said contiguousedge portions and placed around a cylindrical explosive cartridge withthe edges of said groove in abutting relationship to form a closedcylindrical sheath.

2. A molded sheathing for an explosive cartridge comprising a flamequenching composition comprising of the following dry ingredients,sodium bicarbonate, expanded vermiculite, bentonite, bagasse, anddextrine, and 5% water thoroughly intermixed with the dry ingredientsand formed into a plurality of cylindrical segments with their outerconvex surfaces tangent to a common plane, said segments being ofsubstantially uniform thickness and integrally joined along theircontiguous outer edge portions, the inner concave surfaces of saidsegments being separated by a V-shaped groove, each of said innersurfaces comprising a like fractional portion of a circular cylinder,said sheath being adapted to be broken along said contiguous edgeportions and placed around a cylindrical explosive cartridge with theedges of said groove in abutting relationship to form a closedcylindrical sheath.

3. A molded sheathing for an explosive cartridge comprising a flamequenching composition adapted to be formed into a sheath ofsubstantially uniform thickness, the outer surface of said sheathcomprising a plurality of contiguous cylindrical segments tangent to acommon plane, the inner surface comprising a plurality of cylindricalsurfaces concentric to said outer surfaces and separated by V-shapedgrooves, the edge portions of said sheath being partially bounded byradial planes whereby said sheath may be broken into a plurality ofcylindrical segments to form a closed cylindrical sheath with theadjacent edges of said segments in abutting relationship.

IVER C. WOOD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 542,154 Elliott et a1. July 2,1895 2,078,240 Fleming Apr. 27, 1937 2,277,059 Barab Mar. 24, 19422,413,516 Pratt Jan. 27, 1945

